Fuel injection apparatus for internal combustion engine

ABSTRACT

In a fuel injection apparatus for an internal combustion engine, including a fuel pump for feeding fuel from a fuel tank to a fuel distributor, an overflow valve for regulating the pressure of the fuel in said fuel distributor and solenoid valves provided in the same number as the number of cylinders of the engine and connected to said fuel distributor to act as fuel injection valves, said solenoid valves are driven by a variable frequency oscillator and the frequency of said variable frequency oscillator is controlled in accordance with the average quantity of air sucked by the engine per unit time and further said solenoid valves are opened and closed by means of a pulse row independent of the engine speed.

United States Patent [1 1 Suda et al.

[11] 3,786,788 i451 Jan. 22, 1974 [75] Inventors: Toshi Suda, Nagoya;Hideya Fujisawa, Kariya, both of Japan [73] Assignee: Nippondenso Co.,Ltd., Aichi-ken,

Japan 22 Filed: May 24, 1972 21 Appl. No.: 256,256

' Related US. Application Data [63] Continuation-impart of Ser. No.64,766, Aug. 18,

1970, abandoned.

[52] US. Cl......,. 123/322EA, 123/119 R, 123/139 E [51] Int. Cl F02m51/00 [58] Field of Search 123/32 EA, 119 R [56] References Cited UNITEDSTATES PATENTS 3,500,801 3/1970 Long 123/119 R 3,500,802 3/1970Long..... 123/140 MC 3,504,657 4/ 1970 Eichler et a1. 123/32 EA3,659,571 5/1972 Lang 123/32 EA 3,673,989 7/1972 A0no.'.., 123/32 EAPrimary Examiner-Laurence M. Goodridge Assistant Examiner-Cort FlintAttorney, Agent, or Firm-Cushman, Darby &

Cushman [57] ABSTRACT In a fuel injection apparatus for an internalcombustion engine, including a fuel pump for feeding fuel from a fueltank to a fuel distributor, an overflow valve for regulating thepressure of the fuel in said fuel distributor and solenoid valvesprovided in the same number as the number of cylinders of the engine andconnected to said fuel distributor to act as fuel injection valves, saidsolenoid valves are driven by a variable frequency oscillatorv and thefrequency of said variable frequency oscillator is controlled inaccordance with the average quantity of air sucked by the engine perunit time and further said solenoid valves are opened and closed bymeans of a pulse row independent of the engine speed.

2 Claims, 4 Drawing Figures FUEL '- ISWPIBUTOR case/12470;? e

FUEL INJECTION APPARATUS FOR INTERNAL COMBUSTION ENGINE This applicationis a continuation-in-part of the U.S. Ser. No. 64,766 filed on Aug. 18,1970 (now abandoned).

This invention relates to a fuel injection apparatus for an internalcombustion engine and more particularly to an electronically controlledfuel injection apparatus for 1 an external ignition-type internalcombustion engine, in which solenoid valves are provided as fuelinjection valves, and the open period and frequency of said solenoidvalves are controlled thereby to meter fuel.

In a conventionally known fuel injection apparatus of this type, thequantity of intake air per one cycle of the engine is determined fromthe intake pipe pressure, and fuel is metered according to this pressureand supplied to the engine in synchronism with the engine rotation. Sucha system is generally called a speed density system. This prior artsystem is operable on the premise that the intake pipe pressure and thequantity of air supplied per'one cycle of the engine completely matchwith each other. In practice, however, this functional relation betweenthe intake pipe pressure and the quantity of air is variable dependingupon the engine speed,

and thus it becomes necessary to compensate the engine speed. However,the compensation of the engine speed is extremely difficult and theintended object cannot be fully attained. Therefore, the prior artsystem has suffered the fatal drawback that the optimum mixture ratiocannot be obtained at a certain engine speed. Moreover, according tothis prior art system the metering of fuel must be carried out withrespect to two variables, i.e., the engine speed and the intakepressure, and this problem has been solved by a method in which the fuelis injected always in synchronism with the engine speed, therebycontrolling the fuel with respect to the intake pressure. However, sucha method has imposed on the system the restriction that the fuelinjection system injects fuel insynchronism with the enging speed.

In order to obviate the drawbacks described above, the present inventionhas for its objects the provision of a fuel injection apparatus for aninternal combustion engine, in which the flow rate of the intake air inmeasured and the flow rate of fuel is controlled to be optimum for themeasured intake air flow rate by controlling the open period of solenoidvalves, used as fuel injection valves, according to the frequency ofpulses of a predetermined time width to which said open period is fixed,whereby the air-fuel mixture ratio can be exactly adjusted to theoptimum value only by regulating the fuel flow rate per-unit time,without being bothered by the problem of synchronizing the fuelinjection with the engine speed.

The present invention will be described in detail hereunder withreference to the accompanying drawings, in which:

FIG. 1 is an illustrative diagram showing the overall arrangement of oneembodiment of the fuel injection apparatus according to the presentinvention;

FIG. 2 is a view showing one form of the intake air flow rate detectorused in the apparatus;

FIGS. 3(a) and 3(b) are diagram illustrating pulse rows applied to thesolenoid valves respectively;

FIG. 3(0) is a diagram illustrating the relationship between thefrequency and the average fuel flow rate per unit time; and

FIG. 4 is an electrical circuit diagram of the oscillator.

With reference to FIG. 1, the fuel injection apparatus according to thepresent invention includes a fuel tank 1, a fuel pump 2, an overflowvalve 3 and a fuel distributor 4. The fuel pump 2 is driven from anelectric 0 motor not shown to pump fuel from the fuel tank I.

The pumped fuel is partially returned to the fuel tank 1 through theoverflow valve 3 and a fuel return pipe 5, so as to maintain the fuelpressure in conduits 6, 7 and the fuel distributor 4 at a constantvalue. The fuel distributor 4 is connected by fuel injection pipes 8with solenoid valves 9 provided in the same number as the number ofcylinders of the associated engine, so that fuel may be suppliedconcurrently to said solenoid valves 9. The fuel pressure in eachsolenoid valve 9 is the same as that in the fuel distributor 4 and ismaintained constant.

Each solenoid valve 9 is provided in an intake pipe 11 of the engine 10.The intake air of the engine 10 is introduced into the intake pipe 1 1through an intake air flow rate measurer l5 and an intake air flow rateregulator l2, and fed to the respective cylinders, not shown, of theengine 10. The intake air flow rate is regulated by the degree ofopening of a throttle valve 13 in the air flow rate regulator 12 andsaid throttle valve 13 is operatively connected to an accelerator pedal14 through a link mechanism. Thus, it will be seen that the air flowrate is regulated by the accelerator pedal actuated by the driver.

The flow rate of fuel to be supplied to the engine 10 is controlled inaccordance with the flow rate of intake air supplied to the engine, andthe metering of fuel is effected by the operation of the solenoid valves9. Namely, the period of conducting a current through each solenoidvalve 9 at a time is always constant but the frequency of the current isvaried.

FIGS. 3(a) and 3(b) show drive pulses to be applied to the solenoidvalve 9, and FIG. 3(a) exemplifies the case wherein the pulses areapplied at a frequency just twice as large as that of the pulses shownin FIG. 3(b). As may be apparent from these Figures, the avarage fuelflow rate Q, cc/s per unit time is in linear functional relation withthe frequency, as shown in FIG. 3(c), and it will, therefore, beunderstood that the average fuel flow rate Q, cc/s can be controlled byvarying the frequency of the pulses of a completely constant width.

The intake air measurer 15 may, for example, be of the constructionshown in FIG. 2, which comprises a ventri 18, a conical body 19 and aspring 20. As is well known the time-wise average air flow rate Q, cc/sis in proportion to the amount of displacement of the conical body 19.In the present invention, the amount of displacement of the conical body19 is taken out by a link mechanism 21 and said link mechanism 21 isconnected, for example, to a potentiometer (see FIG. 4), whereby thetime-wise average air flow rate 0,, cc/s can be detected as theresistance value of a variable resistor 16 (see FIG. 4). It is to beunderstood that the air flow rate measurer shown in FIG. 2 is onlyillustrative and a known flow meter of the type which detects thetimewise average air flow rate Q, cc/s as a voltage, can of course beused for said air flow rate measurer.

A variation of the time-wise average air flow rate Q, cc/s is detectedas a variation of the electric resistance value as stated above, and itwill be obviously understood that, in this case, the electric resistancevalue may be compensated according to the ambient temperature, theambient atmospheric pressure, the ambient humidity and the throttleacceleration and deceleration as required. By controlling the time-wiseaverage fuel flow rate Q cc/s according to the resistance value, itbecomes possible to control the fuel supply so as to obtain the optimumair-fuel ratio, only by varying the frequency of pulses at a constantpulse width, independently of the engine speed and without the necessityfor synchronizing the fuel supply with the engine speed.

For generating a row of pulses at a frequency variable according to thevariation of the resistance value of the variable resistor 16, asdescribed above, an oscillator 17 is used whic will be describedhereunder:

With reference first to FIG. 4, the oscillator to determine the numberof pulses is comprised of an astable multivibrator 22, a shaping circuit23 for shaping the waveform of the output of astable multivibrator 22, amonostable multivibrator 24 triggered by said shaping circuit 23 todetermine the pulse width and a driving circuit 25 operated by saidoutput to actuate the solenoid valves 9. Reference numeral 26 designatesa battery.

Astable multivibrator 22 is comprised of resistors 22a, 22c, 22c and22h, capacitors 22d and 22f, transistors 22b and 22g, and the variableresistor 16, which are combined in a known manner. If the resistancevalue of the variable resistor 16 is constant, the multivibrator 22 willoscillate at a constant frequency,

but here the resistance value of the variable resistor 16 variesaccording to the air flow rate and hence the frequency varies. Theoutput of the non-stable multivibrator 22 is applied to the shapingcircuit 23 which is composed of resistors 23a, 23b and 23d and atransistor 23c and shapes the waveform. The output of the shapingcircuit 23 is applied to the monostable multivibrator 24 which is of aknown construction and composed of resistors 24a, 24d, 24g, 24h and 24k,capacitors 24c, 24c and 24i, transistors 24b and 24j, and a diode 24f.

The monostable multivibrator 24 generates pulse signals of a constantwidth at a frequency as determined by the aforesaid oscillator andnon-stable multivibrator 22. The pulse signals thus generated areapplied to a driving circuit composed of resistors 25a, 25b, 25c and25c, and transistors 25d and 25f, and the solenoid valves 9 are drivenfor a period corresponding to the pulse width.

Although the manner in which the solenoid valves 9 are controlled hasbeen described above with reference to only one of them, it should beunderstood that the other solenoid valves are controlled in the similarmanner.

As described above, in the fuel injection apparatus for an internalcombustion engine, according to the present invention, a variation ofthe time-wise avarage flow rate of the intake air is detected uponconverting it into a variation of resistance value and a row of pulseswhich are constant in width and variable only in frequency is obtainedaccording to the detected value, and then the pulses are supplied toeach solenoid valve 9 to meter the time-wise average fuel flow rate Opcc/s as a function of said frequency. Therefore, the fuel injectionapparatus has such remarkable advantages that the fuel can be meteredand supplied at a time-wise average flow rate optimum to the time-wiseaverage flow rate of the intake air, that the compensation of the enginespeed is unnecessary which has been necessary in the conventional speeddensity system, that the pulse generator is not required to besynchronized with the engine speed, and that, therefore, the apparatusis extremely simple in construction.

What is claimed is:

l. A fuel injection apparatus for an internal combustion engine,comprising at least one solenoid valve provided in an intake pipe of theengine upstream of an intake valve,

fuel supply means connected to said solenoid valve for supplying fuel ata constant pressure to said solenoid valve, an air flow rate measuringmeans provided in the intake pipe for detecting the flow rate of theintake air and generating an output which varies in accordance with thedetected intake air flow rate, and

an oscillator connected to said air flow rate measuring means in circuitand generating pulses of a constant width at a frequency in accordancewith the output of said measuring means, said oscillator being connectedto said solenoid valve in circuit and said solenoid valve being openedevery time a pulse is generated by said oscillator, whereby the fuel atthe constant pressure is injected and said oscillator including avariable resistor connected to said air flow rate measuring means andbeing variable in resistance value according to the output of saidmeasuring means, an astable multivibrator connected to said variableresistor in circuit and generating pulses at a frequency in accordancewith the resistance value of said variable resistor, and a monostablemultivibrator connected to said astable multi-vibrator in circuit andtriggered by the pulses from said astable multivibrator to generatepulses of a constant width which are applied to said solenoid valve.

2. A fuel injection apparatus according to claim I, wherein saidsolenoid valve is provided in the same number as the number of cylindersof the engine and said fuel supply means includes a distributor capableof supplying the fuel at the constant pressure concurrently to saidrespective solenoid valves.

1. A fuel injection apparatus for an internal combustion engine,comprising at least one solenoid valve provided in an intake pipe of theengine upstream of an intake valve, fuel supply means connected to saidsolenoid valve for supplying fuel at a constant pressure to saidsolenoid valve, an air flow rate measuring means provided in the intakepipe for detecting the flow rate of the intake air and generating anoutput which varies in accordance with the detected intake air flowrate, and an oscillator connected to said air flow rate measuring meansin circuit and generating pulses of a constant width at a frequency inaccordance with the output of said measuring means, said oscillatorbeing connected to said solenoid valve in circuit and said solenoidvalve being opened every time a pulse is generated by said oscillator,whereby the fuel at the constant pressure is injected and saidoscillator including a variable resistor connected to said air flow ratemeasuring means and being variable in resistance value according to theoutput of said measuring means, an astable multivibrator connected tosaid variable resistor in circuit and generating pulses at a frequencyin accordance with the resistance value of said variable resistor, and amonostable multivibrator connected to said astable multi-vibrator incircuit and triggered by the pulses from said astable multivibrator togenerate pulses of a constant width which are applied to said solenoidvalve.
 2. A fuel injection apparatus according to claim 1, wherein saidsolenoid valve is provided in the same number as the number of cylindersof the engine and said fuel supply means includes a distributor capableof supplying the fuel at the constant pressure concurrently to saidrespective solenoid valves.